In the past, there is known an illumination system including a plurality of tile-shaped flat light emitting units (hereinafter referred to as “light emitting units”). In this illumination system, the light emitting units are arranged in a grid shape to adjoin to one another. The adjoining light emitting units are electrically connected to each other through contact points arranged in the mutually adjoining edges of the light emitting units. Electric power is fed from one of the light emitting units to the other via the contact points (see, e.g., Japanese Application Publication No. 2007-536708).
In the light emitting units of this kind, an external conductor such as a lead wire or the like is used to electrically interconnect the adjoining light emitting units. The opposite ends of the external conductor are connected to the contact points of the respective light emitting units. At this time, from the viewpoint of workability, the respective light emitting units are electrically connected to one another by bending the external conductor or by using an external conductor differing in shape.
However, if the light emitting units are arranged in a mutually adjoining relationship, the contact points for electrically interconnecting the adjoining light emitting units are adjacent to each other. This imposes a restriction on the space for accommodation of the external conductor interconnecting the contact points. As a result, even if the external conductor is bent or the external conductor differing in shape is used in conformity with the arrangement of the light emitting units, it is sometimes the case that the workability grows worse due to the insufficient space. The arrangement of the light emitting units is restricted if an attempt is made to secure a sufficient space. It is therefore impossible to arrange the light emitting units with no gap left therebetween. This reduces the degree of freedom in arranging the light emitting units.